Expansion screw with an expansion sleeve having an outer cylindrical surface and regions of greater and lesser wall thickness

ABSTRACT

An expansion screw for being secured in a cavity is threaded at the outer end of its screw portion for co-action with a nut (2) and is provided with an expandable sleeve (10) about its opposite end. The sleeve has an inner profile coacting with an outer profile of the expansion screw for expanding the sleeve when the screw (1) is withdrawn from the sleeve. The outer profile of the screw portion (1) is formed by a plurality of coaxial cones (3-6) with intermediate cylindrical junction portions (7-10), all cones and junction portions being integral with the rest of the screw portion. The inner profile of the sleeve (10) is formed by thickened regions (12), projecting inwards from the inner surface of the sleeve and corresponding to the cylindrical junction portions, and by thinner regions (13) of the sleeve corresponding to the coaxial cones. The thickness of the sleeve is adapted to allow portions of it to be expanded by the cones into bulges (37) extending around the sleeve, the bulges being intended to penetrate into the wall of the cavity for securing the expansion screw therein.

TECHNICAL FIELD

The present invention relates to an expansion screw of the adapted forbeing secured in a cavity and having a screw portion threaded at itsouter end for co-action with a fastening element, e.g. in the form of anut, and which is provided with an expandable sleeve having an outercylindrical surface and an inner profile adapted to coact with the outerprofile of the expansion screw for expanding the sleeve at withdrawal ofthe screw portion from the sleeve, the outer profile of the scew portionbeing formed by a plurality of co-axial cones with intermediatecylindrical junction portions, all the junction portions being madeintegral with the rest of the screw portion.

BACKGROUND ART

Expansion screws for insertion in holes in concrete or rock walls forretaining machine parts are well known, and are available in manydifferent forms. Most often, an expansion screw has one, or only a fewmeans for expanding an associated sleeve, but expansion screws with aplurality of expander cones are known, for example, from GermanPublished Patent Application Nos. 2138246 and 1814485.

Such expansion screws with a plurality of expander cones are intended todistribute the pressure of the sleeve over a large portion of the holewall so that the surface pressure will be kept to a low value. Among theknown expansion screws, are those having a sleeve with a crennelatedprofile. However, such a sleeve has its profile flattened when the screwis loaded and the walls of the hole consist of a very hard material,whereby the screw can then be pulled out of the hole.

SUMMARY OF THE INVENTION

The expansion screw in accordance with the invention is characterized,inter alia, by the inner profile of the sleeve having thickened regionsand attenuated regions. The sleeve thickness is adapted such that whenit is expanded into contact with the wall of the hole, continuedthightening of the screw portion expands a part of the sleeve'sthickened portions into bulges going round the sleeve, these bulgespenetrating into the wall of the hole and primarily contributing toretaining the expansion screw. With the expansion screw in accordancewith the invention, the sleeve at its thickened regions can withstandvery heavy pressure coming on the sleeve when the material in the holewalls is hard. Other forms of the expansion screw are also suitable whenthe walls of the hole consist of soft material with low strength.

BRIEF DESCRIPTION OF DRAWINGS

In the following, embodiments of expansion screws in accordance with theinvention are described with reference to the appended drawing, wherein

FIG. 1 diagrammatically illustrates in section a complete expansionscrew;

FIG. 2 illustrates development of a sleeve of the expansion screw;

FIG. 3 illustrates an expansion screw with different spacings betweenthe thickened regions of the sleeve and the cones of the expansionscrew;

FIG. 4 is an end view of the expansion screw as seen towards itsinnermost end;

FIG. 5 illustrates buckling in the attenuated portions of the sleeve;

FIG. 6 illustrates impressions in the thickened places of the sleeve;

FIG. 7 is a section taken along line B--B through the sleeve in FIG. 6;and

FIG. 8 illustrates an expansion bolt with an expanded sleeve.

BEST MODE FOR CARRYING OUT THE INVENTION

As is apparent from FIG. 1, the expansion screw includes a screw portion1 having an outer end which is threaded in order to co-act with a fixingelement. In the example shown, the screw portion is threaded externallyfor co-action with a nut 2, although it can be alternatively made withan axial hole threaded for co-action with a screw. The screw portion isprovided with a plurality of cones, of which one cone 3, situated at theend opposite the threaded end, is directed with its minor end towardsthe threaded portion of the screw and is terminated at its outermost endby a short cylindrical portion. Three remaining cones 4, 5, 6, aredouble cones with the bases facing each other. Both cones in a doublecone have approximately the same vertex angle, but can also havedifferent vertex angles. In principle, all the bases of the cones havethe same diameter, which is somewhat greater than the diameter of thethreaded portion of the screw. Between the cones are cylindricaljunction portions 7, 8, 9 with approximately the same diameter as thethreaded portion of the screw. All cones and junction portions areintegral with the screw portion 1.

The screw portion 1 is surrounded by a cylindrical expansion sleeve 10,extending over all of the expander cones and up to the nut 2, where aflat washer 11 is suitably placed to distribute the pressure of the nuton the sleeve end.

The expanding sleeve 10, illustrated in cross section in FIG. 1, extendsaround the circumference of the screw portion with the exception of anarrow axial slit extending along the entire length of the sleeve. Thesleeve 10 is substantially cylindrical on its outside surface and formedwith thickened regions 12 projecting inwardly from the inner surface ofthe sleeve and corresponding to the cylindrical junction portions 7-9 ofthe screw portion, the sleeve also being formed with attenuated orthinner regions 13, corresponding to the expander cones 3-6. The sleevecan, for example, be produced from a strip of great extension in thetransverse direction of the shown sleeve, and with said thickenedregions and attenuated regions running along the strip.

A variant of the sleeve 10 can be made with two or more slits, whichseparate the sleeve into several co-acting segments.

As illustrated in FIG. 2, illustrating a development of the sleeve 10,the sleeve is further formed with a plurality of short slits 14 in thelongitudinal direction of the sleeve over the thickened placescorresponding to the cylindrical junction portions 7-9. The sleeve canthus be more easily expanded by the action of the cones than if thecircumference of the sleeve were unbroken.

The expansion bolt with sleeve is intended for insertion in a hole in awall or floor 15, see FIG. 1, and to retain an object 16, e.g. thefoundation for a machine. The form of the fixing means allows it to beinserted in the drilled hole 15 while the object 16 is in place aboveit. Otherwise, the hole can be bored through the hole in the object tobe fixed, while the object is in its intended place. When the nut 2 istightened, the the screw portion 1 is pulled out somewhat from thesleeve 10, the expander cones 3-6 co-acting with the thickened regions12 of the sleeve to expand the sleeve.

The thickness of the sleeve is adapted such that where the expandercones 3-6 press on the thickened regions 12 of the sleeve, and expandthe sleeve into contact with the hole wall, the edges of the thickenedregions, as is shown in FIG. 8, are expanded into bulges 37 extendinground the sleeve 10. Upon continued tightening of the nut, thecompressive force of the expander cones acting on the thickened regionswill be so high that the bulges are pressed into the hole wall, wherebythe entire expansion bolt is kept in the hole with great force.

An expanding sleeve 21 in FIG. 3 can alternatively be made with greaterspacing between the thickened regions 22 than between the expander cones3-6 of the screw portion 1. With this embodiment of the sleeve, movementof the screw portion 1 in the direction of the arrow will cause theexpansion of the sleeve 21 to occur first at the innermost cone 3,thereafter at the next innermost cone 4 etc. This results in increasedcertainty that the pressure of the sleeve on the hole walls primarilyaffects the interior of the hole so that risk of the hole edges beingdamaged is considerably reduced.

As is apparent from the end view of the sleeve 21 in FIG. 4, comparedwith FIG. 3, the sleeve is clipped up at a portion towards its end, anddeformed into a support 23 for the innermost end of the expansion screw.This support 23 determines more accurately the insertion of the sleeveinto the hole in the wall as compared to the action of the nut by itselfon the threaded portion of the expansion screw. All the describedexpanding sleeves are intended to be made with one or more deformedsupports 23.

When the nut 2 is screwed onto the threads of the screw portion 1, seeFIG. 1, the screw will be pulled out of the expanding sleeve 10 withconsequential expansion of the sleeve. Outward pulling of the screwportion presupposes a reaction force in the form of a pressure betweenthe outer edge of the expanding sleeve and the nut 2 with its washer 11.The expansion of the sleeve 10 is determined only by the nut 2tightening down on the threaded end of the screw portion 1, andindependent of whether the sleeve at the beginning of the nut beingtightened down has already become clamped between the cones of theexpansion bolt and the hole walls or not. The nut with its washer willnow also press on the mounted object 16. This is possible since one ofthe attenuated portions 13 of the sleeve, often a portion which does notsurround any expander cone, is deformed in a way apparent from FIG. 5.After the innermost portions of the sleeve 10 have been clamped to thehole walls, both the screw portion 1 and sleeve are stationary.Continued tighening of the nut 2 causes the attenuated portion 13 of thesleeve to be deformed so that the outermost end of the sleeve 10 can bemoved by the nut a further small distance in towards the hole. The nutand associated washer 11 can thereby be screwed so far that sufficientpressure for retaining the object 16 can be obtained.

In a further development of the invention, which is apparent from FIG. 6and the cross section in FIG. 7, the expansion sleeve 31 is formed withindentations 32 in its thickened portions forming grooves at the outersurface of the sleeve and bulges at the inner surface of the sleeve. Thescrew portion 33 in this case has a plurality of double cones 34, thevertex angles of which are substantially equal. The cones in this screwportion have greater extension than in the previously described screwportions, which leads to the cylindrical junction portions 35 betweenthe cones having less diameter than the junction portions in thepreviously described screw portions. The sleeve 31 is made with twoindentations at each cylindrical junction portion, but the sleeve can bemade with some other number of indentations than two at each place.

The indentations 32 have the effect of increasing the expansion of thesleeve when withdrawing the screw portion 33 than with the sleeve in thepreviously described expansion screws. This latter expansion screw istherefore especially well suited for use in rather loose buildingmaterial where sufficiently strong fixing can be obtained with a largeexpansion of the sleeve.

I claim:
 1. An expansion fastener adapted for being secured in a cavitycomprising a screw portion having a threaded end, a nut threaded on saidthreaded end and an expandable sleeve on said screw portion, said sleevehaving an outer cylindrical surface facing a wall of the cavity when thefastener is inserted into the cavity, said screw portion includingintegral, axially spaced conical portions defining intermediatecylindrical portions between the conical portions, said sleeve having aninner surface facing said screw portion and including a wall withthickened regions corresponding to said cylindrical portions to formprojections at said inner surface of said sleeve located betweenadjacent spaced conical portions on said screw portion and thinnerregions between said thickened regions corresponding to said conicalportions to form recesses in said inner surface of said sleeve receivingsaid conical portions, said thinner regions being of reduced thicknesscompared to said thickened regions to permit greater expansion of saidthickened regions than the remainder of the sleeve upon relative axialmovement of said sleeve and screw portion to form outer bulges aroundthe sleeve for pressing against the wall of the cavity to secure thefastener in the cavity, the spacing between said thickened regions ofsaid sleeve being greater than the spacing between said conical portionsof said screw portion.
 2. An expansion fastener as claimed in claim 1wherein said nut bears against said sleeve.
 3. An expansion fastener asclaimed in claim 1 wherein said sleeve is provided with at least onetransverse groove in said outer surface at one of said thickened regionsand a corresponding bulge at the inner surface of said sleeve.
 4. Anexpansion fastener as claimed in claim 2 wherein said sleeve is providedwith longitudinal slits in said thickened regions.
 5. An expansionfastener as claimed in claim 1 wherein said sleeve has a longitudinalslot extending the length of the sleeve.
 6. An expansion fastener asclaimed in claim 1 wherein said sleeve includes an end portion remotefrom the end proximate the threaded end of said screw portion, said endportion of the sleeve being radially deformed to provide a support forsaid screw portion.
 7. An expansion fastener as claimed in claim 1wherein said conical portions each includes frusto-conical sections withfacing bases.